Nuclear magnetic resonance testing of substances to determine the constituents therein is well known in the art. In known devices, the sample is arranged between the poles of a magnet and is enclosed by a wire coil to enable a sample to be subjected to RF electromagnetic pulses of a predetermined frequency. The resulting NMR pulse generated by the nuclei of the sample under test is detected and processed by the NMR device in a well known manner to identify the sample constituents.
In some cases, it is important to determine the constituents of a fluid sample. In such cases, the fluid sample may be placed in a test tube and the test tube placed in the magnetic field in order to subject it to the pulsed electromagnetic field. If the sample in such cases is positioned in a magnetic field in a gap between magnet poles, small spacial nonlinearities in the magnetic field in the gap may distort the signal that is detected. One well known way of avoiding this distortion is to rotate the sample about an axis that is substantially perpendicular to the direction of the magnetic field in the gap. This, in effect, subjects the sample to the spacial average of the magnetic field provided that angular velocity of rotation of the sample is higher than the Larmor radian frequency of the charged particle that is being subjected to analysis in the given magnetic field. One method of rotating the test tube in the prior art is to use an O-ring to couple the test tube to a motor. The motor can then be controlled to rotate the test tube at a desired speed. However, the frictional engagement of the O-ring with respect to the test tube creates problems. If for any reason, resistance is applied to the test tube while it is rotating, the frictional engagement of the O-ring is sufficient to break the test tube. Also, if it is desired to remove the test tube for any reason, the motor must be stopped in rotation because if the test tube were attempted to be removed during rotation, the frictional engagement would again be sufficient to shatter the test tube. In order to avoid these problems, air bearings have been used which allow the test tube to be held in a unit that is rotated by air. It therefore allows the test tube to be removed during rotation. However, it has other disadvantages since it is affected by rotational friction and by the magnetic field in which the test tube is positioned. Further, the speed of rotation of the test tube cannot be accurately adjusted with this air bearing device.
The present invention overcomes the disadvantages of the prior art by enabling a variable speed electric motor to rotate the test tube in such a manner that the operator is permitted to grasp the spinning test tube and remove it from the unit without stopping the driving motor. It is also possible to insert a test tube into the unit while the motor is rotating to bring the test tube up to speed without breaking it. Further, the drive motor can be accurately controlled in rotational speed to cause the test tube to be rotated at any desired speed.
Thus, it is an object of the present invention to provide frictional coupling between an electric motor and a rotating test tube such that the test tube can be inserted in and removed from the rotational unit while it is being operated.
It is also an object of the present invention to utilize multiple point frictional contact between the test tube and the driving device such that the friction necessary to rotate the test tube can be generated and yet enable the test tube to be removed from and inserted in the device while it is rotating.
It is yet another object of the present invention to utilize a coil spring formed in a 360.degree. continuous circle as a frictional engagement device rotating with the driving device and frictionally engaging the test tube.
It is also an object of the present invention to utilize a rotating brush having bristles arranged to circumferentially contact the test tube in frictional engagement to rotate the test tube.
It is still another object of the present invention to provide a frictional engagement between a rotating device and a test tube that can be adjusted to a desired degree of frictional engagement.